Field of the Invention
The present invention relates to microfluidic processing of biological samples and, more particularly, to methods and apparatuses for use in temperature controlled processing of biological samples in a microfluidic device.
Description of the Related Art
Microfluidics refers to a set of technologies involving the flow of fluids through channels having at least one linear interior dimension, such as depth or diameter, of less than 1 mm. It is possible to create microscopic equivalents of bench-top laboratory equipment such as beakers, pipettes, incubators, electrophoresis chambers, and analytical instruments within the channels of a microfluidic device. Since it is also possible to combine the functions of several pieces of equipment on a single microfluidic device, a single microfluidic device can perform a complete analysis that would ordinarily require the use of several pieces of laboratory equipment. A microfluidic device designed to carry out a complete chemical or biochemical analyses is commonly referred to as a micro-Total Analysis System (μ-TAS) or a “lab-on-a chip.”
A lab-on-a-chip type microfluidic device, which can simply be referred to as a “chip,” is typically used as a replaceable component, like a cartridge or cassette, within an instrument. The chip and the instrument form a complete microfluidic system. The instrument can be designed to interface with microfluidic devices designed to perform different assays, giving the system broad functionality. For example, the commercially available Agilent 2100 Bioanalyzer system can be configured to perform four different types of assays—DNA (deoxyribonucleic acid), RNA (ribonucleic acid), protein, and cell assays—by simply placing the appropriate type of chip into the instrument.
In a typical microfluidic system, the microfluidic channels are in the interior of the chip. The instrument interfacing with the chip performs a variety of different functions: supplying the driving forces that propel fluid through the channels in the chip, monitoring and controlling conditions (e.g., temperature) within the chip, collecting signals emanating from the chip, introducing fluids into and extracting fluids out of the chip, and possibly many others. The instruments are typically computer controlled so that they can be programmed to interface with different types of chips and to interface with a particular chip in such a way as to carry out a desired analysis.
Microfluidic devices designed to carry out complex analyses will often have complicated networks of intersecting channels. Performing the desired assay on such chips will often involve separately controlling the flows through certain channels, and selectively directing flows through channel intersections. Fluid flow through complex interconnected channel networks can be accomplished either by building microscopic pumps and valves into the chip or by applying a combination of externally-generated driving forces to the chip. Examples of microfluidic devices with pumps and valves are described in U.S. Pat. No. 6,408,878, which represents the work of Dr. Stephen Quake at the California Institute of Technology. Fluidigm Corporation of South San Francisco, Calif., is commercializing Dr. Quake's technology. The use of multiple electrical driving forces to control the flow through complicated networks of intersecting channels in a microfluidic device is described in U.S. Pat. No. 6,010,607, which represents the work Dr. J. Michael Ramsey performed while at Oak Ridge National Laboratories. The use of multiple pressure driving forces to control flow through complicated networks of intersecting channels in a microfluidic device is described in U.S. Pat. No. 6,915,679, which represents technology developed at Caliper Life Sciences, Inc. of Hopkinton, Mass.
Lab-on-a-chip type microfluidic devices offer a variety of inherent advantages over conventional laboratory processes such as reduced consumption of sample and reagents, ease of automation, large surface-to-volume ratios, and relatively fast reaction times. Thus, microfluidic devices have the potential to perform diagnostic assays more quickly, reproducibly, and at a lower cost than conventional devices. The advantages of applying microfluidic technology to diagnostic applications were recognized early on in development of microfluidics. In U.S. Pat. No. 5,587,128, Drs. Peter Wilding and Larry Kricka from the University of Pennsylvania describe a number of microfluidic systems capable of performing complex diagnostic assays. For example, Wilding and Kricka describe microfluidic systems in which the steps of sample preparation, PCR (polymerase chain reaction) amplification, and analyte detection are carried out on a single chip.
For the most part, the application of microfluidic technology to diagnostic applications has failed to reach its potential, so only a few such systems are currently on the market. Two of the major shortcomings of current microfluidic diagnostic devices relate to cost and to difficulties in sample preparation. Issues related to cost arise because materials that are inexpensive to process into chips, such as many common polymers, are not necessarily chemically inert, thermally stable, or optically transparent enough to be suitable for diagnostic applications. To address the cost issue, technology has been developed that allows microfluidic chips fabricated from more expensive materials to be reused, lowering the cost per use. See U.S. Published Application No. 2005/0019213. However, when chips are reused, issues of cross-contamination from previously processed samples could arise. The best solution may be to overcome the limitations of currently available polymer materials so that a chip can be manufactured inexpensively enough to be disposed of after a single use.
It is an object of the present invention to employ microfluidic devices for the performance of assays, such as PCR, that could be relevant to diagnostic applications. In particular, it is an object of the invention to provide methods and apparatuses based on microfluidic technology that allow PCR amplification and analyte detection to be performed in a cost-effective manner.
These and further objects will be more readily appreciated when considering the following disclosure and appended claims.